Heavy ion beams stopping in tissue consist of primary particles and fragments due to nuclear interactions in the materials presented to the beam. These fragments are a significant component of the dose, especially near the Bragg peak and distal volume. Conventional dosimetry does not identify the fluence, charge, and velocity of these components. Biological effects (e.g., RBE and OER) depend on these quantities rather than on mean LET alone. The present research will continue a comprehensive approach to understanding of the physical interactions of high-energy heavy ion beams to the extent necessary for predicting relevant characteristics of beams used in clinical and biophysical research at the Lawrence Berkley Laboratory BEVALAC. This approach consists of an experimental program and an theoretical program. The experimental program provides complete characterization of the beams by particle identification and direct measurements of fluence and velocity, using a multidetector particle identification spectrometer consisting of time-of-flight telescopes, silicon detector stacks, position-sensitive detectors, pulse-ionization chambers, and scintillation counters. The apparatus has been used to identify nuclear reaction fragments and primary beam particles emerging from a water column along the central axis of the beam, as a function of water thickness. Beams of carbon, neon, silicon, argon, and iron are being studied along their unmodified as well as their range-modulated Bragg curve. Angular distribution measurements of fragmentation and multiple Coulomb scattering, including simulation of tissue inhomogeneities, will follow. The theoretical program develops beam transport calculations to obtain reliable beam models for extension of the results to predicting cell survival in arbitrary beam configurations. Comparison of predicted and measured fluence spectra is used to refine the calculational codes. The results of this research will be incorporated into treatment planning for clinical trials of radiation therapy currently in progress at the BEVALAC.